Methods and systems for promoting ventricular pacing

ABSTRACT

A device and method for multi chamber pacing a patient&#39;s heart having heart failure and intrinsic conduction, wherein ventricular tracking is used to pace the ventricle when the sinus rate exceeds a preset atrial maximum tracking rate. The ventricular tracking pacemaker increases the range of pacing the ventricle. The ventricular tracking minimizes the loss of ventricular pacing caused by intrinsic conduction when the sinus rate is below an atrial maximum tracking rate, and it induces a new ventricular pacing behavior for sinus rates above the atrial maximum tracking rate without any significant pacing hysteresis as the sinus rate returns towards the lower rate limit.

RELATED PATENT DOCUMENTS

[0001] This application is a division of U.S. patent application Ser.No. 10/062,048 filed on Jan. 31, 2002, which is a division of U.S.patent application Ser. No. 09/420, 679, filed on Oct. 19, 1999, nowU.S. Pat. No. 6,415,180, which is a continuation-in-part of U.S. patentapplication Ser. No. 08/833,281, filed on Apr. 4, 1997, now U.S. Pat.No. 5,983,138. U.S. Pat. No. 5,983,138 is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

[0002] I. Field of the Invention This invention relates generally to adevice and method for pacing a patient's heart and more particularly toa device and method for improving the hemodynamic performance ofpatients suffering from heart failure through dual chamber pacing. Thepatient in need of improving hemodynamic performance may suffer from,for example, congestive heart failure (CHF), or other heart failurerequiring pacing even though intrinsic PR conduction is present. Thedevice includes a means for tracking an R-wave associated with intrinsicconduction in a ventricle of the patient's heart. The method includestracking a sensed R-wave for a predetermined RV delay interval and thenstimulating the ventricle if a P-wave is sensed during the presetsimultaneous Post Ventricular Atrial Refractory Period (PVARP) interval.

[0003] II. Discussion of the Related Art

[0004] Typically, a patient suffering from a higher degree of AV-blockor an AV conduction disorder is implanted with a conventional atrialtracking (DDD or VDD) pacemaker suited for pacing the ventricle. Such apacemaker is designed to pace the ventricle after a pre-set AV delay,synchronous with the intrinsic atrial rate. The purpose of thesepacemakers is to make sure that heart beats are properly timed and notomitted. Intrinsic rhythm is favorable over paced rhythm for bothhemodynamic and economic (battery conservation) reasons. It is alsoimportant and necessary to prevent pacing the ventricle during thevulnerable period for inducing arrhythmia immediately following anintrinsic ventricular beat. Hence, ventricular pacing is inhibited whenintrinsic conduction from the SA node causes an R-wave to be sensedprior to the scheduled ventricular pace.

[0005] Patients suffering from congestive heart failure (CHF), forexample, either do not exhibit heart block at all or often only sufferfrom a first degree AV-block or a slightly prolonged delay intervalbetween the depolarization of the atrium and the depolarization of theventricle. Recent research has shown that acute hemodynamic performance,exercise tolerance and quality of life of CHF patients can be improvedby a pre-excitation of the ventricles with pacing following normal sinusbeats. Patients benefiting from pre-excitation of the ventriclesexperience a return of heart failure symptoms immediately upon omissionof pre-excitation pacing. Thus, for these patients, it is important thatthe paced pre-excitation of the ventricle be performed continuously inorder to improve the contraction pattern, even though intrinsic beatswould occur slightly later if there were no pacing. When pacing apatient suffering from CHF, it is highly undesirable to omit pacing whenit is supposed to occur.

[0006] When pacing the heart of a CHF patient having normal intrinsic(PR) conduction, although continuous pacing is desirable, use of aconventional atrial tracking dual chamber pacemaker completely inhibitsventricular pacing when the intrinsic atrial rate (hereinafter the sinusrate) rises above a preprogrammed atrial maximum tracking rate (AMTR).These pacemakers also exhibit an undesirable pronounced pacinghysteresis, wherein ventricular pacing is not resumed until the sinusrate falls below a ventricular inhibition threshold rate (VIR). Also, inthese pacemakers, a premature ventricular contraction (PVC) may inhibitventricular pacing when the sinus rate exceeds the VIR.

[0007] It would be advantageous to eliminate the pacing hysteresis,while extending the limit or MTR for pacing of the ventricle. However,this is not possible with the conventional atrial tracking multi-chamberpacemaker. A CHF patient, for example, has an elevated sinus rate inorder to maintain normal cardiac output despite reduced cardiac pumpingefficiency and, therefore, requires a high atrial MTR. Together with anelevated sinus rate, many such patients also have prolonged PR intervalsand correspondingly prolonged retrograde conduction intervals requiringlong PVARP intervals. The required long PVARP intervals prevent trackingof retrograde P-waves, thereby reducing pacemaker mediated tachycardia(PMT). In conventional atrial tracking pacemakers, the highest allowableatrial MTR is determined in part by the length of the PVARP interval,which may limit the atrial MTR to a rate that is below the normal rangeof sinus rates in the CHF patient. Hence, use of a conventional atrialtracking dual chamber pacemaker would not allow continuous ventricularpacing above the atrial MTR. Therefore, there is a need for a dualchamber pacemaker and a method of operating the same that may be used topace the failing heart of a patient having intrinsic conduction, whereinthe pacemaker provides for continuous pacing of the ventricle at a sinusrate that exceeds an atrial maximum tracking rate and does not exhibitpacing hysteresis below the MTR. The present invention addresses thisneed.

SUMMARY OF THE INVENTION

[0008] The purpose of the present invention is to provide a device andmethod of pacing continuously, without hysteresis, the ventricles of apatient's failing heart having intrinsic conduction even when the sinusrate rises above a preset atrial maximum tracking rate. Conventionaldual chamber pacemakers commonly have a combination of dual chambersensing, atrial sensing, ventricular sensing, dual chamber pacing,atrial pacing, ventricular pacing, and atrial tracking. A conventionaldual chamber pacemaker may be modified according to the presentinvention to include a ventricular tracking mode and thereby increasethe range of pacing therapy. When used with a patient having intrinsic(PR) conduction, the ventricular tracking mode minimizes the loss ofventricular pacing output as the sinus rate rises above a preset atrialMTR. As the atrial MTR is exceeded by the sinus rate, the ventriculartracking pacemaker restores a Wenckebach-like pacing behavior, therebycontinuing ventricular pacing.

[0009] During this Wenckebach-like pacing, the ventricular trackingpacemaker paces the ventricle due to atrial tracking unless a legitimateP-wave is sensed during a preset post ventricular atrial refractoryperiod (PVARP). A legitimate P-wave refers to a signal or wave thatcorresponds to an intrinsic atrial depolarization. When a legitimateP-wave is sensed during the PVARP, the ventricular tracking pacemakertracks a preceding sensed R-wave (due to intrinsic PR conduction) andpaces the ventricle after a preset delay interval, hereinafter referredto as the RV delay. Alternatively the ventricular pace can occur after apreset delay from the P-wave sensed during PVARP, hereinafter referredto as the refractory atrial to ventricular (RAV) delay. As the sinusrate continues to increase, the sinus rate reaches a 2:1 ventriculartracking rate up to a ventricular MTR or limit at which pointventricular pacing is inhibited. The conventional dual chamber pacemakerignores legitimate P-waves sensed during PVARP and does not pace theventricle above the atrial MTR. With the ventricular tracking pacemaker,as the sinus rate decreases from the ventricular MTR, there is nosignificant pacing hysteresis commonly found in the conventional atrialtracking pacemakers.

[0010] The ventricular tracking pacemaker includes a means for sensingan atrial event and transmitting a signal associated with the sensedatrial event, means for sensing a ventricular event and transmitting asignal associated with the sensed ventricular event, means for trackinga P-wave, means for tracking an R-wave, means for selectivelystimulating a preselected ventricle of the patient's heart, and a meansfor controlling the selective stimulation of the ventricle. The meansfor controlling the stimulation is electrically coupled to the sensing,tracking and stimulating means. The means for controlling thestimulation controls the stimulation to the preselected ventricle inaccordance with a timing sequence which is dependent upon the trackedventricular and tracked atrial events.

[0011] In the preferred embodiment, the means for controlling determinesthe intrinsic ventricular rate from the signal corresponding to sensedventricular events. If the intrinsic ventricular rate is greater thanthe preset ventricular maximum tracking rate, the means for controllinginhibits the stimulation to the ventricle.

OBJECTS

[0012] It is accordingly a principal object of the present invention toprovide a multi chamber pacemaker for pacing the selected ventricles ofa patient suffering from heart failure but having intrinsic PRconduction, wherein the ventricle may be paced at a rate that is abovean atrial maximum tracking rate.

[0013] A further object of the present invention is to provide a multichamber pacemaker for pacing the selected ventricles of a patient,wherein the selected ventricles are paced a preset time after an R-waveis tracked by the pacemaker.

[0014] Another object of the present invention is to provide a method ofmulti chamber pacing that paces the selected ventricles a preset timeafter detecting an intrinsic conduction transmitted from the ventricles.

[0015] Yet another object of the present invention is to provide amethod of multi chamber pacing which paces the ventricles a preset timeafter a P-wave is sensed during a PVARP interval following a sensedR-wave, wherein pacemaker-mediated tachycardia is prevented if theP-wave is due to retrograde conduction.

[0016] Still another object of the present invention is to provide apacemaker that may pace the ventricle above the atrial MTR, whereinthere is no significant pacing hysteresis when the atrial rate returnsto a lower rate limit.

[0017] These and other objects, as well as these and other features andadvantages of the present invention will become readily apparent tothose skilled in the art from a review of the following detaileddescription of the preferred embodiment in conjunction with theaccompanying drawings and claims and in which like numerals in theseveral views refer to corresponding parts.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a graph showing the intrinsic atrial (sinus) rate inrelation to the paced ventricular rate of a conventional atrial trackingpacemaker, employed when a patient has complete heart block;

[0019]FIG. 2 is a graph showing the intrinsic atrial rate in relation tothe paced ventricular rate of a conventional atrial tracking pacemakerwhere the patient has normal intrinsic (PR) conduction;

[0020]FIG. 3 is a graph showing the intrinsic atrial rate in relation tothe paced ventricular rate of a conventional atrial tracking pacemakerwhere the patient has experienced a Premature Ventricular Contraction(PVC);

[0021]FIG. 4 is a graph showing the intrinsic atrial rate in relation tothe paced ventricular rate of a ventricular tracking pacemaker where thepatient has normal intrinsic (PR) conduction;

[0022]FIG. 5 is a comparison graph illustrating the increased range ofpacing therapy utilizing a ventricular tracking pacemaker compared tothe conventional atrial tracking pacemaker;

[0023]FIG. 6 is a plot showing a sensed P-wave and tracked R-wave inconjunction with a ventricular tracking pacemaker's PVARP and RVintervals;

[0024]FIG. 7 is a plot showing a sensed P-wave and tracked R-wave inconjunction with a ventricular tracking pacemaker's PVARP and RVintervals, wherein a P-wave is tracked during the RV interval;

[0025]FIG. 8 is a plot showing a tracked R-wave in conjunction with aventricular tracking pacemaker's PVARP and RV intervals, wherein aP-wave is neither sensed nor tracked during the RV interval;

[0026]FIG. 9 is a plot showing a tracked R-wave in conjunction with aventricular tracking pacemaker's PVARP and RV intervals, wherein asecond R-wave is tracked during the RV interval;

[0027]FIG. 10 is a plot showing a sensed P-wave and tracked PVC inconjunction with a ventricular tracking pacemaker's PVARP and RVintervals;

[0028]FIG. 11 is a plot showing a sensed P-wave and tracked PVC inconjunction with a ventricular tracking pacemaker's PVARP and RVintervals, wherein a second R-wave is tracked during the RV interval;

[0029]FIG. 12 is a plot showing a sensed retrograde P-wave and trackedPVC in conjunction with a ventricular tracking pacemaker's PVARP and RVintervals;

[0030]FIG. 13 is a plot showing a sensed P-wave and tracked R-wave inconjunction with a ventricular tracking pacemaker's PVARP and RVintervals, wherein the sinus rate is between the VIR and AMTR;

[0031]FIG. 14 is a plot showing a sensed P-wave and tracked PVC inconjunction with a ventricular tracking pacemaker's PVARP and RVintervals, wherein the sinus rate is between the VIR and AMTR;

[0032]FIG. 15 is a plot showing a sensed P-wave and tracked R-wave inconjunction with a ventricular tracking pacemaker's PVARP and RVintervals, wherein the sinus rate is between the AMTR and VMTR;

[0033]FIG. 16 is a plot showing a sensed P-wave and tracked PVC inconjunction with a ventricular tracking pacemaker's PVARP and RVintervals, wherein the sinus rate is between the AMTR and VMTR;

[0034]FIG. 17 is a plot showing a sensed P-wave and tracked R-wave inconjunction with a ventricular tracking pacemaker's PVARP and RVintervals, wherein the sinus rate is between the AMTR and VMTR and theventricular tracking reaches a 2:1 blocking point;

[0035]FIG. 18 is a plot showing a sensed P-wave and tracked R-wave inconjunction with a ventricular tracking pacemaker's PVARP and RVintervals, wherein the sinus rate exceeds the VMTR;

[0036]FIG. 19 is a plot showing a sensed P-wave and tracked R-wave inconjunction with a ventricular tracking pacemaker's PVARP, RV, and RAVintervals, when delay priority timing is in effect;

[0037]FIG. 20 is a plot showing a sensed P-wave and tracked R-wave inconjunction with a ventricular tracking pacemaker's PVARP, RV, and RAVintervals, when delay priority timing is in effect and a P-wave issensed during the PVARP interval and after the RV interval;

[0038]FIG. 21 is a plot showing a sensed P-wave and tracked R-wave inconjunction with a ventricular tracking pacemaker's PVARP, RV, and RAVintervals, wherein the RAV interval expires before the RV interval;

[0039]FIG. 22 is a plot showing a sensed P-wave and tracked R-wave inconjunction with a ventricular tracking pacemaker's PVARP, RV, and RAVintervals, wherein the RAV interval expires before the RV interval and asecond R-wave is tracked during the RV interval;

[0040]FIG. 23 is a block diagram showing the components of theventricular tracking pacemaker of the present invention;

[0041]FIG. 24 is a flowchart showing the algorithm used by theventricular tracking pacemaker of the present invention to trackintrinsic conduction from the ventricle and accordingly pace theventricle when rate priority timing is in effect; and

[0042]FIGS. 25 and 26 are flowcharts showing two algorithms that may beused by the ventricular tracking pacemaker of the present invention totrack intrinsic conduction from the ventricle and accordingly pace theventricle when delay priority ventricular tracking is in effect.

DEFINITIONS

[0043] PVC Premature Ventricular Contraction

[0044] LRL Lower Rate Limit

[0045] PVARP Post Ventricular Atrial Refractory Period

[0046] PR time between depolarization of the atrium and ventricle

[0047] VIR Ventricular Inhibition Rate

[0048] AMTR Atrial Maximum Tracking Rate

[0049] VMTR Ventricular Maximum Tracking Rate

[0050] CHF Congestive Heart Failure

[0051] SAV Sensed Atrial to Ventricular delay

[0052] RAV Refractory Atrial to Ventricular delay

[0053] RV time delay between sensing ventricular conduction and pacingthe ventricle

[0054] URL Upper Rate Limit

[0055] MTR Maximum Tracking Rate

DETAILED DESCRIPTION

[0056] Referring first to FIGS. 1-3, these graphs show the intrinsicatrial rate or sinus rate of a patient in relation to the pacedventricular rate or output of a conventional atrial tracking pacemakerwhen used in a variety of patient conditions. FIG. 1 illustrates theventricular pacing rate by a conventional atrial tracking pacemaker,pacing the heart of a patient having a complete block of all intrinsicconduction. As the sinus rate increases, the pacemaker's pacing ratetracks the atrial rate until the pacing rate reaches a pre-programmedatrial maximum tracking rate (AMTR) at 15. At this point, as the atrialrate continues to increase, there is a fall-off in the ventricularpacing rate attributable to a pacemaker mediated atrial Wenckebachbehavior at 12. During this period, some of the pacemaker's ventricularpacing pulses are inhibited by the pacemaker to prevent pacing theventricle at a rate above the AMTR. As the sinus rate at 16 continues toincrease above the AMTR, the average ventricular pacing rate slowlydecreases until a 2:1 ratio between the atrial rate and ventricularpacing occurs, as at 14.

[0057]FIG. 2 illustrates the pacing behavior of a conventional atrialtracking pacemaker, when the patient's heart has normal intrinsic (PR)conduction. The ventricular pacing rate tracks the intrinsic atrial rateuntil the atrial rate reaches an AMTR as at 15. Once the sinus rateexceeds the pre-programmed AMTR, the pacemaker inhibits ventricularpacing until the intrinsic atrial rate decreases to a rate below theAMTR corresponding with the Ventricular Inhibition Rate (VIR). The VIRis equal to the rate corresponding to the sum of the PVARP and PRintervals. When the sinus rate decreases to a rate equal to the VIR,ventricular pacing resumes until the intrinsic atrial rate again reachesthe AMTR. As seen in FIG. 2, when pacing a patient (having intrinsicconduction) with a conventional atrial tracking pacemaker, there is apronounced pacing hysteresis as represented at 18. This pacinghysteresis limits the range of pacing therapy to the patient. Unlikepacing a patient having complete heart block, the atrial trackingpacemaker will not pace a patient having intrinsic conduction when thesinus rate exceeds the AMTR. This is significant because many of thepatients having intrinsic conduction who could benefit fromuninterrupted ventricular pacing typically have elevated sinus rates(above the AMTR) to compensate for the reduced pumping efficiency oftheir failing heart.

[0058] Additionally, when the patient's heart has intrinsic conduction,the ventricular pacing rate by the pacemaker may even be inhibited at arate below the AMTR. FIG. 3 illustrates that the range of pacing therapyof a conventional atrial tracking pacemaker may be further limited by apremature ventricular contraction (PVC). When a PVC occurs, and thesinus rate is above the VIR, ventricular pacing may be inhibited by theatrial tracking pacemaker until the sinus rate falls below the VIR,thereby further limiting the range of available pacing therapy.

[0059] Referring to FIGS. 4 and 5, the sinus rate of a patient havingnormal intrinsic conduction is shown in relation to the resulting pacedventricular rate of a ventricular tracking pacemaker of the presentinvention. Significantly, the range of pacing therapy is expanded usinga ventricular tracking pacemaker of the present invention on a patienthaving intrinsic conduction. When the sinus rate exceeds a preset atrialmaximum tracking rate (AMTR) as at 15, ventricular tracking restores aWenckebach-like behavior at 22 (hereinafter referred to as ventricularWenckebach). During ventricular Wenckebach, ventricular pacing occursdue to atrial tracking, until a sensed atrial event falls within thepreset PVARP allowing an intrinsically conducted R-wave to occur, whichinhibits ventricular pacing for that sinus beat. To restore ventricularpacing when the sensed atrial event falls within the preset PVARP, thesubsequent intrinsically conducted R wave is tracked and the ventricleis paced after a preset pacing delay, subject to other variablesdiscussed in further detail below. As the sinus rate (represented bydotted line 16) increases above the AMTR as at 15, the averageventricular pacing rate slowly decreases due to Wenckebaching at 22until the sinus rate reaches a 2:1 ventricular tracking rate as at 24.Once the sinus rate exceeds the preset ventricular maximum tracking rate(VMTR), ventricular pacing is inhibited. Importantly, unlike theresulting behavior of an atrial tracking pacemaker, there is nosignificant hysteresis as the sinus rate falls below the VMTR or AMTR ofthe ventricular tracking pacemaker.

[0060]FIGS. 6-22 are various plots illustrating the occurrence of asensed P-wave and the resulting tracked R-wave plotted over time withrespect to the ventricular tracking pacemaker's preset timing intervalsand varying sinus rates. The time of occurrence of the ventricularpacing stimulation is indicated by labeled block “V” at 30. The time ofoccurrence of a sensed P-wave is indicated by labeled block “P” at 32. Atracked P-wave is indicated by labeled block “P*” at 34. A time ofoccurrence of a sensed R-wave due to intrinsic conduction is indicatedby labeled block “R” at 36 and a time of occurrence of a sensed PVC isindicated by labeled block “PVC” as at 38 and the time of occurrence ofa sensed retrograde P-wave (Retro P) is indicated at 46 (see FIGS.10-12, 14, and 16). Several preset timing intervals are positionedrelative to the time at which the P wave, R-wave or a PVC are sensed.The preset post ventricular atrial refractory period (PVARP) timinginterval is indicated at 40, the preset ventricular pacing delayinterval (RV) at 42, the sensed atrial to ventricular delay (SAV) at 44,the intrinsic conduction (PR) interval is indicated at 48, the presetatrial maximum tracking rate interval (AMTRI) is indicated at 50 and thepreset refractory atrial to ventricular delay (RAV) is indicated at 51.

[0061] Two alternative timing sequences of the ventricular trackingpacemaker are illustrated by the various Figures. Only one timingsequence can be in effect during a particular cardiac cycle, however,those skilled in the art will appreciate that alternative timingsequences can be used on different cardiac cycles. The choice and use ofthe alternate timing sequence is programmable in the ventriculartracking pacemaker. The first timing sequence, referred to as the “ratepriority” timing sequence or “rate priority” ventricular tracking, pacesthe ventricles after a tracked R-wave at a preset ventricular trackingrate. An alternate timing sequence, referred to as the “delay priority”timing sequence or “delay priority” ventricular tracking, paces theventricles after a tracked R-wave to achieve a preset delay between arefractory P-wave sense and the ventricular pace, but not faster than apreset ventricular tracking rate. The delay priority timing sequence isan alternate of the more general rate priority timing sequence. Asfurther described below, FIGS. 6-18 illustrates the general “ratepriority” timing sequence, which applies also to “delay priority”ventricular tracking, except that the ventricular tracking rate is notconstant for “delay priority” timing. FIGS. 19-22 illustrate thealternate “delay priority” timing sequence.

[0062] Referring to FIG. 6, the rate priority timing sequence of theventricular tracking pacemaker is illustrated. An R-wave 36 is sensed,initiating the PVARP 40 and RV 42 intervals. Since a P-wave 32 is sensedduring the PVARP 40 interval, the ventricle is paced after a tracked RVdelay 42. If a P*-wave 34 is sensed after the PVARP 40 but before theexpiration of the RV 42 delay, then the ventricle is not paced until theexpiration of a sensed atrial to ventricular delay 44 as shown in FIG.7. Further, when a P-wave 32 is not sensed during the PVARP 40 interval,the ventricle is not paced at the end of the RV 42 interval, (see FIG.8). Also, if an R-wave 36 is sensed during the RV delay 42 interval,then the RV delay 42 interval is restarted (see FIG. 9). Hence, normallythe ventricle will be paced according to rate priority ventriculartracking a predetermined amount of time after an R-wave is sensed if aP-wave is also sensed during a PVARP and RV interval, unless otherconditions are present.

[0063]FIGS. 10-12 show the tracking behavior of the ventricular trackingpacemaker when the sinus rate is between the lower rate limit (LRL) andthe ventricular inhibition rate (VIR). When the sinus rate is in thisrange, the ventricular tracking pacemaker may be programmed to pace theventricle according to 1:1 atrial tracking, unless a PVC causes a sensedP-wave to fall in PVARP or causes a sensed retrograde P-wave withinPVARP. In such a case, when a PVC causes a sensed P-wave to fall inPVARP or causes a sensed retrograde P-wave within PVARP, ventriculartracking takes over for pacing of the ventricle. FIG. 10 illustrates asensed PVC 38 starting the preset PVARP 40 and RV delay 42. Since alegitimate P-wave 32 is sensed during the PVARP 40 and the intrinsic PR48 conduction delay extends beyond the RV delay 42, the ventricle ispaced at the end of the RV delay 42 interval. FIG. 11 illustrates a PVCcausing a sensing of an R-wave 36 during the RV delay 42 interval andrestarting of the RV delay 42 interval. When the sinus rate is betweenthe lower rate limit (LRL) and the ventricular inhibition rate (VI R), aPVC 38 may cause a sensed retrograde P-wave 46. As shown in FIG. 12, aPVC cannot cause a pacemaker mediated tachycardia due to ventriculartracking. The PVC starts an RV 42 interval and the sensed retrogradeP-wave 46 enables a ventricular tracking pace at 30, which in turncauses a second retrograde P-wave that is not followed by a ventricularpace because a second RV 42 interval is not initiated at the ventricular30 pace.

[0064] Referring now to FIGS. 13 and 14, these plots illustrate thegeneral reaction of the ventricular tracking pacemaker when the sinusrate is between the ventricular inhibition rate and the atrial MTR.Again in this rate range the ventricular tracking pacemaker may pace theventricle in accordance with 1:1 atrial tracking, however since a singlePVC 38 could cause continuous inhibition of ventricular pacing, it isnecessary to pace the ventricle in accordance with ventricular tracking,unless a P*-wave 34 is sensed outside of the PVARP 40. When an R-wave 36due to intrinsic PR 48 conduction is sensed, wherein the sinus rate isgreater than the ventricular inhibition rate, the ventricular trackingis triggered to restore ventricular pacing. A sensed R-wave 36 andP-wave 32 during PVARP 40 causes the pacing of the ventricle after thepreset RV delay 42 (see FIG. 13). When a PVC is sensed and causes theintrinsic P-wave to be sensed during PVARP, ventricular tracking istriggered (see FIG. 14). If a PVC occurs such that a P-wave is sensedoutside the PVARP, pacing of the ventricle after the RV delay isinhibited and normal atrial tracking occurs (see FIG. 14). Hence, it canbe seen that in this rate range the ventricular tracking pacemakerdiffers from a conventional DDD pacemaker. While a single PVC can causean atrial tracking pacemaker to inhibit ventricular pacing, theventricular tracking pacemaker will pace the ventricle after the RVdelay as described above.

[0065]FIGS. 15-17 show the general tracking behavior of the ventriculartracking pacemaker when the sinus rate is between the atrial MTR (AMTR)and the ventricular maximum tracking rate (VMTR). When the sinus rate isin this range, the pacer goes into a ventricular Wenckebach behavior,during which an intrinsically conducted R-wave occasionally inhibits aventricular pace. The ventricular tracking pacemaker will continue togenerate Wenckebach ventricular pacing behavior as long as the RVinterval is less than the AMTRI (see FIG. 15). FIG. 16 shows that a PVCin this range can cause an extra Wenckebach cycle, wherein theventricular tracking eventually restores ventricular pacing. Eventually,ventricular tracking reaches a 2:1 ventricular rate tracking (see FIG.17). As illustrated in FIG. 18, once the sinus rate exceeds the VMTR,ventricular pacing is inhibited, because every RV interval is restartedby an intrinsic R wave before pacing can occur.

[0066]FIGS. 19-22 illustrate the alternate timing sequence of theventricular pacemaker that dynamically extends the time of ventricularpacing after the RV delay expires, to thereby maintain a preset delaybetween the atrial sense and ventricular pace due to ventriculartracking. This timing sequence of the ventricular pacemaker is referredto as delay priority ventricular tracking and is illustrated generallyin FIGS. 19 and 20. An R-wave 36 is sensed, initiating the PVARP 40 andRV 42 intervals. When a P-wave 32 is sensed during the PVARP 40interval, a preset refractory atrial to ventricular delay (RAV) isinitiated. As shown in FIG. 19, when the RV 42 interval ends before theexpiration of the RAV 51 delay, the ventricle is paced at the end of theRAV 51 delay, as long as the RAV 51 delay is less than the intrinsic PR48 interval. This has the effect of extending the duration of the RV 42interval by the RV extension 52 period indicated by the highlightedportion of the box.

[0067]FIG. 20 illustrates the delay priority timing sequence when theP-wave 32 is sensed during the PVARP 40 interval after the tracked RVdelay 42 has ended. The RV delay 42 ends without pacing the ventriclebecause the P-wave 32 is not sensed during the RV delay 42. Instead, theventricle is paced after the expiration of the RAV 51 interval, which isinitiated by the P-wave 32 sensed during the PVARP 40 interval. Again,this has the effect of extending the duration of the RV 42 interval bythe RV extension period.

[0068]FIGS. 21 and 22 illustrate that the delay priority timing sequencereverts to the rate priority timing sequence when the delay prioritytiming sequence would result in pacing the ventricle before the end ofthe RV interval. As shown in FIG. 21, an R-wave 36 is sensed, initiatingthe PVARP 40 and RV 42 intervals. When a P-wave is sensed during thePVARP 40 interval, the RAV 51 delay is initiated. Since the RAV 51 delayends before the RV 42 interval, the ventricle is paced after the RV 42interval, as long as it expires before the intrinsic PR 48 intervalexpires. When the RV 42 interval expires after the intrinsic PR 48interval, as illustrated in FIG. 22, an intrinsic R-wave 36 is detected,which restarts the RV 42 interval.

[0069] Hence, the ventricle will be paced according to delay priorityventricular tracking a predetermined amount of time after a P-wave issensed during PVARP following an R-wave, but not faster than the RVdelay, unless other conditions are present. Those skilled in the artwill appreciate that since delay priority ventricular tracking only hasthe effect of extending the RV interval, all the rate priority timingsequences shown in FIGS. 6-18 also apply to the ventricular pacemakerhaving a delay priority timing sequence when the RV interval in thoseFigures is replaced by an extended RV interval (the RV interval plus RVextension period) when it applies as shown in FIGS. 19 and 20.

[0070] Referring next to FIG. 23, the preferred embodiment of theinvention is shown generally in block diagram, wherein the cardiacstimulator or ventricular tracking pacemaker 110 (enclosed by a dottedline) operatively connects to a patient's heart 112 by electricalconductors 114, 116, and 118 embodied in a pacing lead 120 for atrialand ventricular dual chamber pacing. The first end of the pacing lead122, inserted into the patient's heart 112, branches into an atrialbranch 124 and a ventricular branch 126. The atrial branch 124 connectsto a first set of stimulating and sensing electrodes 128 which areadapted to be disposed in the right atrium of the heart 112 and isarranged to sense the occurrence of P-wave activity relating to atrialevents. The ventricular branch 126 connects to a second set ofstimulating and sensing electrodes 130, which are adapted to be disposedin either the right or left ventricle of the heart. Those skilled in theart will appreciate that other pacing and/or sensing leads of suitableknown construction may be coupled to the cardiac stimulator and disposedin the patient's heart.

[0071] The atrial branch 124 is connected by electrical conductor 114 toan atrial sense amplifier 132 which detects P-waves associated withatrial events. The resulting atrial event signal is fed to an input of amicroprocessor-based controller 134. In a similar fashion, theventricular branch 126 is operatively coupled by conductor 116 to aventricular sense amplifier 136. The ventricular sense amplifier 136functions to detect R-wave activity relating to ventriculardepolarization. The signal representing the R-wave activity is then fedto an input of a microprocessor-based controller 134.

[0072] The microprocessor-based controller 134 is programmed to operatein any one of a plurality of known pacing modes and includes aventricular tracking mode of the present invention. Also coupled to themicroprocessor 134 is a timing circuit 150, atrial tracking circuit 152,and ventricular tracking circuit 154. The microprocessor 134 has bothRAM (random access memory) 138, and ROM (read only memory) 140 forstoring programs and data, which allows: the processing of the sensedsignals, triggering the pulse generator 142, determining a sinus ratefrom the sensed signals, analyzing the sensed signals, and storingvarious information derived from the analysis. While FIG. 23 depicts apacing/sensing lead in the right atrium and right ventricle, thoseskilled in cardiac rhythm management systems will appreciate that otherleads of known construction may be positioned in other areas of theheart and coupled to corresponding amplifiers and theMicroprocessor-based controller.

[0073] The microprocessor 134 controls the cardiac stimulating pulsesdelivered by pulse generator 142 to one or both of the first and secondstimulating electrodes 128 and 130 (depending upon the pacing modeselected). An external programmer 144 having a microprocessor andassociated memory may transmit information in a conventional way througha telemetry link 146 and transmission receiver 148 of the cardiacstimulator's microprocessor. Using the programmer 144 and the telemetrylink 146, operating parameter values for the pacemaker 110 can bedelivered to it by a cardiologist for setting the cardiac cycle pacingparameter values to be utilized, including various timing intervals.Cardiac stimulating devices capable of telemetering various statusinformation including selecting the pacing parameters and mode(determined by the physician) are commercially available from, forexample, Cardiac Pacemakers, Inc., St. Paul, Minn.

[0074]FIG. 24 shows an algorithm that may be used by the ventriculartracking pacemaker of the present invention for rate priorityventricular tracking to track intrinsic conduction from the ventricleand accordingly pace the ventricle over a broader pacing range.Initially, a signal is transmitted through sensing lead 120 from theatrium of a patient's heart and P-waves from the signal are identifiedand tracked (see block 200). A signal is also transmitted throughsensing lead 120 corresponding to events of the ventricle of a patient'sheart and R-waves from the signal are identified (see block 202). Theclock timer of the timing circuit 150, the RV delay interval and thePVARP interval are initialized in conjunction with the sensing of anR-wave (see blocks 204 and 206). Once the time on the clock timerexceeds the preset RV delay (see decision block 208) then the ventricleis paced at block 214 if: a P-wave is sensed during the PVARP interval,a sensed atrial to ventricular delay has not been started to track aP-wave sensed outside of PVARP (see decision blocks 210 and 212), and asecond R-wave is not sensed during the RV delay interval (see decisionblock 210). If an R-wave is sensed during the RV delay interval, thetimer is reset and the RV and PVARP intervals are re-initiated (see loop216). If a P-wave is tracked by an SAV delay, the sensing and trackingis re-initiated (see loop 218). The ventricles will not be pacedaccording to this algorithm, unless a P-wave is sensed during PVARP (seeloop 218).

[0075]FIGS. 25 and 26 show algorithms that may be used by theventricular pacemaker of the present invention for “delay priority”ventricular tracking. The algorithm shown in FIG. 25 is implemented whenthe RV interval is constrained to be greater than or equal to the PVARP.The algorithm shown in FIG. 26 is implemented when the RV interval isallowed to be less than the PVARP. Referring to FIG. 25, initially asignal is transmitted through sensing lead 120 from the atrium of apatient's heart and P-waves from the signal are identified and tracked(see block 270). A signal is also transmitted through sensing lead 120corresponding to events of the ventricle of the patient's heart andR-waves from the signal are identified (see block 272). The clock timerof the timing circuit 150, the RV delay interval and the PVARP intervalare initialized in conjunction with the sensing of an R-wave (see blocks274 and 276). During a time not greater than the RV interval (seedecision block 278) it is determined whether a P-wave is sensed duringthe PVARP interval (see decision block 280). If a P-wave is sensedduring the PVARP interval, then a RAV interval is initiated from thecurrent time (see block 282). Also during the time when the time of theclock timer is not greater than the RV interval, if an R-wave is sensed(as at decision block 284), then the clock timer is reset (see loop286). When the time on the timer exceeds the RV interval, as at 278,then it is determined whether the P-wave is being tracked by an SAVdelay (see decision block 290) and whether a P-wave has been sensedduring PVARP (see decision block 292). If the P-wave is being tracked byan SAV delay or a P-wave has not been sensed during PVARP, thenventricular tracking is reset (see loop 288). If the P-wave is not beingtracked by an SAV delay and a P-wave has been sensed during PVARP, thenthe clock timer is compared to the RAV interval as at decision block294. When the time of the clock timer exceeds the RAV interval, then theventricle is paced as at block 298, unless an R-wave is sensed first(see block 296), which then resets the clock timer without pacing theventricle and the algorithm is then repeated (see loop 286).

[0076] Referring now to FIG. 26, an algorithm is shown that may be usedby the ventricular pacemaker of the present invention for “delaypriority” ventricular tracking when the RV interval is allowed to beless than the PVARP. Initially, a signal is transmitted through sensinglead 120 from the atrium of a patient's heart and P-waves from thesignal are identified and tracked (see block 230). A signal is alsotransmitted through sensing lead 120 corresponding to events of theventricle of a patient's heart and R-waves from the signal areidentified (see block 232). The clock timer of the timing circuit 150,the RV delay interval and the PVARP interval are initialized inconjunction with the sensing of an R-wave (see blocks 234 and 236). Ifthe time on the timer is not greater than RV, and a P-wave is sensedduring PVARP, then an RAV interval is initiated from the current timeand it is then determined whether the time on the timer is greater thanthe RV as long as a new R-wave has not been sensed (see decision blocks250, 252, 238 and 248).

[0077] Once the time on the clock timer exceeds the preset RV delay (seedecision block 238) then it is determined whether the P-wave is beingtracked by an SAV delay (see decision block 240). If the P-wave is beingtracked by an SAV delay, then ventricular tracking is reset (see loop264). If the P-wave is not being tracked by an SAV delay at decisionblock 240, then it is determined whether a P-wave has been sensed duringPVARP (see decision block 242). If a P-wave is sensed during PVARP at242 and the time is greater than the RAV interval (block 246), then theventricle is paced at block 262. If a P-wave has not been sensed duringPVARP at block 242, it is then determined whether the time is greaterthan PVARP (see decision block 244). When the time exceeds the PVARP asat 244, then ventricular pacing is reset (see loop 264) unless a P-waveis sensed during PVARP (see block 256). In that case, an RAV delay isinitiated at the current time (see block 258), and after the time on thetimer is greater than the RAV interval (see decision block 246), theventricle is paced at 262 as long as a new R-wave has not been sensed(see decision block 260). If a new R-wave is sensed during the algorithm(see decision blocks 248, 254, and 260), then the clock timer is resetand the RV and PVARP delays are re-initiated (see loop 249).

[0078] Another algorithm that may be used by the ventricular trackingpacemaker of the present invention for delay priority ventriculartracking includes a pre-programmed modification of the conventionalatrial tracking timing intervals after a sensed R-wave so that theatrial tracking rate is temporarily increased to the ventricular maximumtracking rate. When a pacing cycle follows a ventricular pace, thenormal atrial tracking timing intervals are implemented by thepacemaker. However, when a pacing cycle follows a sensed R-wave, theatrial tracking timing interval resets for the next cycle to thefollowing: the atrial maximum tracking rate interval is set to equal thepreset RV interval, the SAV interval is set to equal the preset RAVinterval, and the PVARP interval set to be less than the time of the RVinterval minus the PR interval. With these reset timing intervals, aconventional atrial tracking algorithm is used to control ventricularpacing for the cycle (a conventional atrial tracking algorithm mayinclude the following: when a P-wave is sensed outside of PVARP, the SAVinterval is initiated and when it expires, the ventricle is paced unlessthe maximum tracking rate interval has not expired, in which case theventricular pace is delayed until the end of the maximum tracking rateinterval. After the cycle, the RV interval, SAV interval and PVARPintervals return to their preset intervals. Those skilled in the artwill appreciate that this algorithm will produce the same pacingbehavior as that described above in conjunction with FIG. 26.

[0079] It is recognized that the length of the RV delay and RAVintervals may be varied relative to other timing intervals of thepacemaker to control the ventricular tracking behavior of theventricular tracking pacemaker. Further, the varied length of the RVdelay and RAV intervals may also depend on features of a conventionalatrial tracking pacemaker.

[0080] This invention has been described herein in considerable detailin order to comply with the patent statutes and to provide those skilledin the art with the information needed to apply the novel principles andto construct and use such specialized components as are required.However, it is to be understood that the invention can be carried out byspecifically different devices, and that various modifications, both asto the equipment details and operating procedures, can be accomplishedwithout departing from the scope of the invention itself.

What is claimed is:
 1. A pacing method, comprising: providing aplurality of atrioventricular delays, the plurality of atrioventriculardelays comprising a sensed atrioventricular delay; providing a postventricular atrial refractory period (PVARP) associated with a pacingtiming sequence; delivering a bi-ventricular pacing therapy using thepacing timing sequence; detecting an event that disrupts ventricularpacing; modifying the pacing timing sequence; delivering thebi-ventricular pacing therapy using the modified pacing timing sequenceto mitigate the disruption of ventricular pacing; sensing an intrinsicatrial depolarization occurring beyond the PVARP during delivery of themodified bi-ventricular pacing therapy; initiating the sensedatrioventricular delay relative to the intrinsic atrial depolarization;and pacing at least one ventricle following the sensed atrioventriculardelay.
 2. The method of claim 1, wherein providing the plurality ofatrioventricular delays comprises providing the sensed atrioventriculardelay, the sensed atrioventricular delay associated with intrinsicatrial depolarization events sensed beyond the PVARP.
 3. The method ofclaim 1, wherein providing the plurality of atrioventricular delayscomprises providing a refractory atrioventricular delay, the refractoryatrioventricular delay associated with intrinsic atrial depolarizationevents sensed within the PVARP.
 4. The method of claim 1, whereindetecting the event that disrupts ventricular pacing comprises detectingone atrial event occurring within the PVARP.
 5. The method of claim 1,wherein detecting the event that disrupts ventricular pacing comprisesdetecting two or more atrial events occurring respectively within two ormore successive PVARPs.
 6. The method of claim 1, wherein detecting theevent that disrupts ventricular pacing comprises detecting an intrinsicventricular depolarization.
 7. The method of claim 1, wherein detectingthe event that disrupts ventricular pacing comprises detecting apremature ventricular contraction.
 8. The method of claim 1, whereinmodifying the pacing timing sequence comprises adjusting the PVARP. 9.The method of claim 1, wherein modifying the pacing timing sequencecomprises adjusting the PVARP for two or more successive cycles.
 10. Themethod of claim 1, wherein modifying the pacing timing sequencecomprises decreasing the PVARP.
 11. The method of claim 1, whereinmodifying the pacing timing sequence comprises ignoring the PVARP. 12.The method of claim 1, wherein using the modified pacing timing sequencecomprises restoring the ventricular pacing.
 13. The method of claim 1,wherein using the modified pacing timing sequence comprises avoidingpacing hysteresis as an intrinsic atrial rate decreases below a maximumtracking rate.
 14. The method of claim 1, wherein using the modifiedpacing timing sequence comprises restoring the ventricular pacingfollowing a premature ventricular contraction.
 15. The method of claim1, wherein using the modified pacing timing sequence comprises restoringthe ventricular pacing following a transient increase in heart rateabove a maximum tracking rate.
 16. The method of claim 1, wherein usingthe modified pacing timing sequence comprises the restoring ventricularpacing as an intrinsic atrial rate decreases below a maximum trackingrate.
 17. The method of claim 1, wherein using the modified pacingtiming sequence comprises pacing at a rate below an upper rate limit.18. The method of claim 1, wherein using the modified pacing timingsequence comprises implementing a ventricular tracking pacing protocol.19. The method of claim 18, wherein implementing the ventriculartracking pacing protocol comprises: initiating an ventricular pacingescape interval relative to a sensed intrinsic ventriculardepolarization; and delivering bi-ventricular pacing following thepacing escape interval if an intrinsic atrial depolarization is sensedfollowing the intrinsic ventricular depolarization.
 20. The method ofclaim 1, wherein delivering the bi-ventricular pacing therapy comprises:selecting one or more ventricles selected from a right ventricle and aleft ventricle; and pacing the selected one or more ventricles.
 21. Themethod of claim 1, wherein delivering the bi-ventricular pacing therapycomprises pacing a left ventricle.
 22. The method of claim 1, whereindelivering the bi-ventricular pacing therapy comprises pacing a leftventricle and a right ventricle.
 23. The method of claim 1, whereinusing the modified pacing timing sequence comprises interrupting themodified pacing sequence if an intrinsic ventricular depolarization isdetected during implementation of the modified pacing timing sequence.24. The method of claim 1, wherein using the modified pacing timingsequence comprises: scheduling delivery of bi-ventricular pacing basedin part on detection of an atrial event occurring within the programmedPVARP; and canceling the bi-ventricular pacing if an intrinsicventricular depolarization is detected.
 25. The method of claim 1,wherein using the modified pacing timing sequence comprises avoidingpacemaker mediated tachycardia.
 26. A cardiac rhythm management system,comprising: a lead system comprising electrodes for electricallycoupling to a heart, the electrodes configured to deliver stimulationpulses to right and left ventricles of the heart and to sense electricalactivity of the heart; and a pulse generator coupled to the lead system,the pulse generator configured to implement a plurality ofatrioventricular delays, including a sensed atrioventricular delay,deliver a bi-ventricular pacing therapy using a pacing timing sequencehaving a post ventricular atrial refractory period (PVARP), detect anevent that disrupts ventricular pacing, modify the pacing timingsequence to mitigate the disruption of ventricular pacing, controldelivery of a bi-ventricular pacing therapy using the modified pacingtiming sequence, sense an intrinsic atrial depolarization occurringbeyond the PVARP during delivery of the bi-ventricular pacing therapy,initiate the sensed atrioventricular delay relative to the intrinsicatrial depolarization, and pace at least one ventricle following thesensed atrioventricular delay.
 27. The system of claim 26, wherein thesensed atrioventricular delay is associated with intrinsic atrialdepolarization events sensed beyond the PVARP.
 28. The system of claim26, wherein the pulse generator is configured to implement a refractoryatrioventricular delay, the refractory atrioventricular delay associatedwith intrinsic atrial depolarization events sensed within the PVARP. 29.The system of claim 26, wherein the event that disrupts ventricularpacing comprises one atrial event occurring within the PVARP.
 30. Thesystem of claim 26, wherein the event that disrupts ventricular pacingcomprises two or more atrial events occurring respectively within two ormore successive PVARPs.
 31. The system of claim 26, wherein the eventthat disrupts ventricular pacing comprises an intrinsic ventriculardepolarization.
 32. The system of claim 26, wherein the event thatdisrupts ventricular pacing comprises a premature ventricularcontraction.
 33. The system of claim 26, wherein the pulse generator isconfigured to modify the pacing timing sequence by adjusting the PVARP.34. The system of claim 26, wherein the pulse generator is configured tomodify the pacing timing sequence by decreasing the PVARP.
 35. Thesystem of claim 26, wherein the pulse generator is configured to modifythe pacing timing sequence by ignoring the PVARP.
 36. The system ofclaim 26, wherein the modified pacing timing sequence is configured toavoid pacing hysteresis as an intrinsic atrial rate decreases below amaximum tracking rate.
 37. The system of claim 26, wherein the modifiedpacing timing sequence is configured to restore ventricular pacingfollowing a premature ventricular contraction.
 38. The system of claim26, wherein the modified pacing timing sequence is configured to restoreventricular pacing following a transient increase in heart rate above amaximum tracking rate.
 39. The system of claim 26, wherein the modifiedpacing timing sequence is configured to restore ventricular pacing as anintrinsic atrial rate decreases below a maximum tracking rate.
 40. Thesystem of claim 26, wherein the modified pacing timing sequence isconfigured to pace at a rate below an upper rate limit.
 41. The systemof claim 26, wherein the modified pacing timing sequence comprises aventricular tracking pacing protocol.
 42. The system of claim 26,wherein the pulse generator is configured to interrupt the delivery ofthe bi-ventricular pacing therapy using the modified pacing sequence ifan intrinsic ventricular depolarization is sensed during implementationof the modified pacing timing sequence.
 43. The system of claim 26,wherein the modified pacing timing sequence is configured to avoidpacemaker mediated tachycardia.
 44. A cardiac rhythm management system,comprising: means for providing a plurality of atrioventricular delays,the plurality of atrioventricular delays comprising a sensedatrioventricular delay; means for providing a post ventricular atrialrefractory period (PVARP) associated with a pacing timing sequence;means for delivering a bi-ventricular pacing therapy using the pacingtiming sequence; means for detecting an event that disrupts ventricularpacing; means for modifying the pacing timing sequence; means fordelivering the bi-ventricular pacing therapy using the modified pacingtiming sequence to mitigate the disruption of ventricular pacing; meansfor sensing an intrinsic atrial depolarization occurring beyond thePVARP during delivery of the modified bi-ventricular pacing therapy;means for initiating the sensed atrioventricular delay relative to theintrinsic atrial depolarization; and means for pacing at least oneventricle following the sensed atrioventricular delay.
 45. The system ofclaim 44, further comprising means for detecting one atrial eventoccurring within the PVARP.
 47. The system of claim 44, furthercomprising means for adjusting the PVARP.
 48. The system of claim 44,further comprising means for adjusting the PVARP for two or moresuccessive beats.
 49. The system of claim 44, further comprising meansfor decreasing the PVARP.
 50. The system of claim 44, furthercomprising: means for selecting one or more ventricles from a rightventricle and a left ventricle; and means for pacing the selected one ormore ventricles.
 51. The system of claim 44, further comprising meansfor pacing a left ventricle.
 52. The system of claim 44, furthercomprising means for pacing a left ventricle and a right ventricle. 53.The system of claim 44, further comprising means for interrupting themodified pacing sequence if an intrinsic ventricular depolarization isdetected during implementation of the modified pacing timing sequence.54. The system of claim 44, further comprising means for avoidingpacemaker mediated tachycardia.
 55. A pacing method, comprising:providing a plurality of atrioventricular delays, the plurality ofatrioventricular delays comprising a sensed atrioventricular delay;providing a post ventricular atrial refractory period (PVARP) associatedwith a pacing timing sequence; delivering a bi-ventricular pacingtherapy using the pacing timing sequence; detecting an event thatdisrupts ventricular pacing; adjusting PVARP to mitigate the disruptionof ventricular pacing; delivering the bi-ventricular pacing therapyusing the adjusted PVARP.